By Ryan Paul
November 21, 2008 - 09:53AM CT

Virtualization is a practical way of making the most of underutilized computing resources in data centers, but virtualizing an entire general purpose operating system needlessly consumes a lot of memory and other resources. To address this problem, developers have created tools that generate "Just Enough Operating System" (JeOS) software appliances—lightweight platform images that contain barely enough operating system components and software to serve specific functions.

One of the early leaders in this area is rPath, a North Carolina firm that was launched in 2005 by prominent former Red Hat engineers. The company created a web-based appliance construction tool called rBuilder that can be used to make specialized JeOS images. It leverages rPath's advanced package management system—called Conary—which supports file-based dependency resolution and a variety of other compelling features.

The rBuilder tool allows you to select specific packages from rPath's repository that you want to include in your operating system image. Then, rBuilder will automatically pull in the required dependencies needed to run the software. You can also import your own software by uploading a DEB/RPM package or a compressed zip/tar archive. After you create a JeOS recipe, you can instruct it to generate a self-contained image in a wide variety of formats, including installable or live ISO images, raw disk images, VMware images, and even Amazon EC2 images.

The rBuilder tools were originally to operate with rPath's own flavor of Linux, but the developers have steadily been adding support for additional distributions. This year, rBuilder has gained support for Ubuntu and SUSE Linux Enterprise Server. The latest addition is CentOS, a free distribution based on Red Hat Enterprise Linux. These additions—and the large number of supported output formats—give rBuilder an edge over some competing services that have recently launched.